The present invention relates in general to acoustic pulse response measuring and more particularly concerns novel apparatus and techniques for noninvasively obtaining a signal representative of the airways of a subject or of the acoustic reflection properties of a conduit or cavity. The invention is believed to be especially useful in evaluating the condition of human airways, for noninvasively determining the normal geometry, and the location of obstructions or leaks in a conduit, such as a sewer, water or gas pipe, and for providing a signal representative of the geometry of voice-producing regions for different phonemes helpful in teaching the deaf to speak.
For background information reference is made to an article entitled "Airway geometry by analysis of acoustic pulse response measurements" in the Journal of Applied Physiology for September 1977 beginning at page 523 listing Andrew C. Jackson et al. as authors and identifying the prior work of applicant. Reference is also made to an article entitled "Mechanical Response of the Lungs at High Frequencies" in Journal of Biomechanical Engineering for May 1978 beginning at page 57 by applicant and another and the following article entitled "Canine Pulmonary Input Impedance Measured by Transient Forced Oscillations" by applicant and others. Reference is also made to a paper by applicant el al. entitled "Airway Area by Acoustic Reflections Measured at the Mouth" published on pages 749-58 of JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATORY, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY (1980), portions of which are reproduced herein.
A typical prior art approach mentioned in the first cited article involves a steady-state measurement of the driving point acoustic impedance essentially at the airway opening of a subject excited by a pressure wave in the low bass frequencies determined by measuring the ratio of pressure to velocity at the opening at the excitation frequency. That article also makes reference to measuring impedance in this manner at still higher frequencies. While these measurements are interesting, it is difficult to associate the measurement results with meaningful physical conditions, such as abnormal constriction in the lungs. Furthermore, making the measurements is time-consuming for the subject, difficult and time-consuming for the experimenter, requires at least two pressure transducers needing tedious calibration and averages the results over many breaths, rather than providing information about the instantaneous configuration.
Accordingly, it is an important object of this invention to provide methods and means for providing a signal representative of the physical characteristics of conduits or cavities.
It is a further object of the invention to achieve the preceding object noninvasively.
It is still another object of the invention to achieve one or more of the preceding objects while overcoming one or more of the disadvantages noted above.
It is still a further object of the invention to provide an output signal containing characteristics that may be relatively easily evaluated to determine meaningful physical characteristics of the conduit or cavity.
It is a further object of the invention to achieve one or more of the preceding objects with respiratory measurements.
It is still another object of the invention to achieve one or more of the preceding objects with conduit measurements to provide meaningful information on leaks and/or obstructions.
It is still a further object of the invention to achieve one or more of the preceding objects with relatively low energy short duration acoustic pulses that do not damage the subject being examined according to the invention.
It is still a further object of the invention to achieve one or more of the preceding objects with a technique that provides a signal in form suitable for processing to provide acoustic impedance, or cross-sectional area, as a function of a distance that is especially useful in locating changes produced by abnormal openings or obstruction helpful in diagnosing the existence of the abnormal conditions.
It is still a further object of the invention to achieve one or more of the preceding objects with apparatus that is relatively inexpensive, reliable, rapid, easy to operate by relatively unskilled personnel and is relatively compact.